PHENOMENA OF INHERITANCE 281 



not entirely conclusive, and this question may 

 for the present be regarded as an open one. 

 However there is good evidence that the fac- 

 tors for the determination of sex and of sex- 

 linked characters are distributed in the same 

 way as the "sex chromosomes" are, and it 

 would be a surprising thing if these two phe- 

 nomena should be found not to be related 

 causally. 



Another case of sex-linked inheritance is 

 found in an abnormal condition in man known 

 as haemophilia, which is characterized by a de- 

 ficiency in the clotting power of the blood, and 

 consequently by excessive bleeding after in- 

 jury. "Bleeders" are almost always males, 

 though the defect is always transmitted to a 

 son from his mother who does not usually show 

 the defect because it appears in females only 

 when both parents were affected. The man- 

 ner of inheritance of this character is exactly 

 similar to the inheritance of white eyes in 

 Drosophila and is in all probability due to 

 similar causes. 



One of the most striking cases of sex-linked 

 inheritance is that form of color blindness 



